The Edinger-Westphal nucleus (EW) has classically been associated with the preganglionic parasympathetic innervation of the orbit. Recent investigations, however, show that the connections of EW are more complex than previously thought. EW neurons in the cat have brain stem and spinal projections, but there are few EW cells that project to the orbit; the majority of ciliary ganglion (CG) afferents appear to lie outside EW. In the monkey, CG afferents appear to be absent in EW, but their distribution within the nucleus and their overlap with EW neurons projecting to spinal cord is unclear. This variation of CG afferents between species and the complex pattern of connectivity of EW leaves many issues about the location and projections of orbital parasympathetic afferents unresolved. The proposed experiments address several of these questions by anatomically localizing and immunocytochemically characterizing afferents to CG in cat and monkey. Specific projects will: 1. Use retrograde transport methods to localize CG afferent neurons in cat and monkey. The use of multiple retrograde tracers in the same experiment will make it possible to determine whether the same neurons that project to the orbit have additional central projections to spinal cord or brain stem nuclei. 2. Use immunocytochemical techniques to identify neuropeptides in relation to CG afferents. In the bird, CG afferents in EW contain both substance P and enkephalin. In the cat EW neurons also demonstrate substance P as well as cholecystokinin-like immunoreactivity; whether these neuropeptides are present in cells that project to CG is unknown. The nature or distribution of neuropeptides in monkey EW is also unknown. Immunocytochemical techniques will therefore be used to study the distribution of substance P, enkephalin, somatostatin, and cholecystokinin in EW and surrounding brain. Combined retrograde transport-immunocytochemical studies will make it possible to directly determine whether these neuropeptides are present in CG afferent neurons. 3. Characterize neuropeptide distribution in human EW. Immunocytochemical methods will be used in human autopsy material to study the distribution of cells that demonstrate neuropeptide immunoreactivity in the region of EW. This pattern of staining will be compared to the CG afferent distribution demonstrated in the monkey. The proposed series of experiments will advance our understanding of the organization of parasympathetic control of the orbit by identifying brain stem neurons that project to CG. In addition, the combined retrograde transport and immunocytochemistry will make it possible to localize and identify neuropeptides that may play an important role in orbital parasympathetic funtion.